The invention relates to well screens, and particularly to plastic well screens which, as compared to screens made of stainless steel, offer advantages of low cost and light weight. In some situations, they can offer superior corrosion resistance. Although it is possible to make a low cost screen by simply slotting the outer surface of a plastic pipe, such a screen which would have an appearance like the screen in U.S. Pat. No. 3,358,781 would not have the resistance to clogging provided by metal or plastic screens having tapered wires welded to longitudinal rods so as to form V-shaped slots. Such slots, which are disclosed in Johnson U.S. Pat. No. 2,046,458, prevent clogging since the slot openings diverge inwardly and release any particles that are small enough to pass through the entrance to the slot openings. U.S. Pat. No. 2,933,137 discloses a plastic pipe where holes and slots are either cut into tubular sections or the pipe is wound on a mandrel having spring biased tapered pins to form the openings. U.S. Pat. No. 3,327,865 discloses several ways of producing screens with tapered openings using a composite of material layers. European Patent Application No. 6830 filed July 3, 1979 shows short lengths of plastic well screen sections which have V-shaped slots. Although formation by molding is noted, there is no showing of how this would be accomplished. Since the element includes axially extending openings for bolts, the mold would be very complicated and expensive. A co-pending application Ser. No. 119,279 filed Feb. 7, 1980 and assigned to a common assignee discloses a plastic screen with V-shaped slots formed by an external laser beam which is focused so as to undercut the surface. The resulting product is quite satisfactory for its purpose, but the laser slotting technique is somewhat slow and expensive.